Thesis Defense Announcement
To:  The George Mason University Community

Candidate: Atit Patel
Program: M.S. in Biology
Date:   Thursday, April 9, 2015 
Time:   11:00 AM
Place:  George Mason University
             Fairfax Campus

Exploratory Hall, Room 3302            

Thesis Director: Dr. Daniel N. Cox

Thesis Committee:  Dr. Geraldine Grant, Dr. Ed Otto
A copy of the thesis will be available in the Mercer Library.  All are invited to attend the defense.

MicroRNAs (miRNAs) are a class of short, non-coding RNAs (~22 nucleotides) that function as critical post-transcriptional regulators of gene expression. miRNA-mediated gene regulation has been implicated across numerous species and in a wide variety of tissues with functional role in diverse biological processes including embryonic development, stem cell division, germline specification, neuronal morphogenesis and cancer. Drosophila melanogaster dendritic arborization (da) neurons have emerged as an exceptional model for miRNA studies. We have previously demonstrated that the K box miRNAs, including miR-2b/miR-13b regulate the expression of genes required to restrict dendritic branching. To elucidate the molecular bases of K box miRNA-mediated regulation of dendritic development, we employed bioinformatics strategies to identify putative mRNA targets of miR-2b/miR-13b based on inverse correlation expression analyses.  Candidate K-box target mRNAs were phenotypically validated using the GAL4-UAS system and live confocal microscopy to analyze dendritic morphology. Dendritic architecture was quantitatively evaluated based on three criteria including total dendritic length, number of branches and branch density as a function of length. To further quantitatively assess miR-based regulation of putative target genes that produced significant increases in dendritic branching morphology, we conducted target mRNA expression validation studies and confirmed that these K box miRNAs regulate the expression of noc, Tab2, spas and CG4911 in modulating class-specific dendritic homeostasis. In contrast to the K box miRNAs, which regulate the expression of genes required to restrict dendritic branching, we identified miR-279 as one miRNA that functions by regulating the expression of genes required to promote dendritic growth and branching via gain-of-function analyses.  Overexpression of miR-279 in multiple da neuron subclasses results in overall reductions in dendritic growth and branching, whereas MARCM loss-of-function analyses reveal a cell autonomous role for miR-279  in promoting dendritic branching via gain-of-function analyses.  To further characterize the role of miR-279, we conducted cell autonomous MARCM clonal analyses on miR-279 mutants which revealed concomitant reductions in overall growth and branching, but significant increases in branch density.  These analyses suggest that miR-279 may play a role in coordinating class-specific dendritic outgrowth and branching to achieve homeostatic branch density in neurons with complex dendritic arbors.